Preparation of pig iron samples for spectral analysis

ABSTRACT

A portion of liquid pig iron tapped directly from the furnace is centrifuged until solidification is completed. The centrifuge is lined with refractory material to prevent solidification of the metal while flowing. The sample produced has an approximately homogeneous structure and is subjected to spectral analysis.

United States Patent [1 1 Hancart et a1.

[ Dec. 18, 1973 PREPARATION OF PIC IRON SAMPLES FOR SPECTRAL ANALYSIS lnventorsz Jules Hancart, Bressoux; Ivan Houbart, Chenee, both of Belgium Centre National de Recherches Metallurgigues Centrum voor research in de Metallurgie, Brussels, Belgium Filed: June 7, 1972 Appl. No.: 260,593

Related US. Application Data Continuation-impart of Ser. No. 876,959, Nov. 14, 1969, abandoned.

Assignee:

Foreign Application Priority Data Nov. 15, 1968 1' Luxembourg 57328 US. Cl 356/74, 73/DIG. 9, 164/4,

Int. Cl G0lj 3/00, GOln 1/00 Primary Examiner-David Schonberg Assistant ExaminerV. P. MCGraw Att0rneyMarvin R. Stern et a1.

[57] ABSTRACT A portion of liquid pig iron tapped directly from the furnace is centrifuged until solidification is completed. The centrifuge is lined with refractory material to prevent solidification of the metal while flowing. The sample produced has an approximately homogeneous structure and is subjected to spectral analysis.

1 Claim, 6 Drawing Figures l /////////l7/l PREPARATION OF PIG IRON SAMPLES FOR SPECTRAL ANALYSIS This Application is a Continuation-in-Part of copending Application Ser. No. 876,959, filed Nov. 14, I969 now abandoned, by Jules I-Iancart and Ivan I-Ioubart, for Preparation of pig iron samples. The benefit of the filing date of that application is hereby claimed.

The invention relates to the prepartion of samples of pig iron intended to be submitted to spectral analysis, for instance of the arc spectrum or X-ray fluorescence spectrum One 'known method of spectral analysis of pig iron samples consists in setting up an electric are under an atmosphere of argon between a solid pig iron sample which has been suitably prepared and a suitable electrode, and then analysing in vacuum the radiation emitted by the electric are formed in this manner.

In one current technique concerning this method of measurement, the pig iron samples are taken in the liquid state, for instance in the casting channel of a blast furnace, cast immediately in ingot moulds, and conveyed to the laboratory to be prepared and analysed there at once. This method, however, is not without a certain number of disadvantages which may alter its effectiveness and its accuracy.

It is in particular well known that the carbon content cannot be found accurately when the sample, prepared as has been described above, is constituted of grey iron, since the electric discharge is not stable there, as a result of the presence of considerable areas of graphite. To obtain samples constituted of white pig, which is more homogeneous than grey pig, these samples are cast in the form of thin plates, which are rapidly cooled. Nevertheless, this abrupt coolingfrequently leads to cracking of the samples, which cannot then be submitted to spectral analysis, since the oxygen occluded in the cracks would disturb the electrical discharge.

Attempts have already been made to overcome these disadvantages by subjecting the ingot in the laboratory to a remelting operation followed by centrifuging, in order to obtain a sample with a more homogeneous structure.

However, this method has two main disadvantages:

firstly, the increase in the duration of the operations for preparing the sample, since it is necessary to effect the remelting in the laboratory, and secondly, in the course of this remelting there is considerable risk of change in the chemical composition of the sample (oxidation of the carbon, pollution due to the crucible, and so on).

The invention provides a method of preparing a pig iron sample, in which one collects in the liquid, form (for instance by means of a ladle) directly at the outlet of a furnace, such as a blast-furnace or a remelt apparatus (cupola furnace), a sample of the pig iron to be analysed; this sample is transferred immediately in liquid form (that is to say without having had the time for its solidification to begin, and/or withouthaving been submitted to remelting) to a centrifuge, where it is centrifuged until it solidifies, after which it may be subjected directly to spectral analysis.

This method has a number of advantages in comparison with the known methods which have previously been used. As the centrifuger is placed in the immediate proximity of the source of liquid pig iron (e.g., blast-furnace or cupola) it is no longer necessary to cast an ingot and then to remelt it for the purpose of centrifuging it. The centrifugedsample is obtained directly in the course of work, which represents a considerable saving in time. Moreover, the omission of the remelting operation greatly reduces any risk of change in the composition of the pig iron.

In addition to this, there is the entirely unexpected, and still unexplained result, in the case of grey pig, that the distribution of the graphite is sufficiently homogeneous for the carbon content to be determinable by the method of spectral analysis by electric arc. There is furthermore the remarkable and equally unexpected fact that samples of white pig no longer crack.

The invention also provides a centrifuging device by which it is possible to put into operation the method described above. The centrifuging device comprises an enclosure having a filling orifice; means for rotating the said enclosure about an axis preferably passing through the said orifice; at least two conduits, which form extensions of the enclosure, each being terminated at its free end by an orifice provided with a sealing cover, and each having its longitudinal axis substantially perpendicular to the axis of rotation of the enclosure, all the conduits being arranged substantially in the same plane; and a refractory lining covering the internal wall of the enclosure and side walls of the conduits.

In accordance with a particularly advantageous variation of the device, the refractory lining covering the internal wall of the enclosure and the conduits is terminated at the ends of the conduits by a portion which is slightly bent back (or folded) towards the centre of the conduit, which has the effect of breaking the active force of the molten metal and of reducing any risk of deterioration of the sealing cover by the metal.

The invention will be described further with reference to the accompanying drawings, which are given by way of example, are not intended to be restrictive, and are not drawn to scale.

FIG. 1 is a diagrammatic vertical section through part of a centrifuging device;

FIG. 2 is a plan view of the device, with ancillary apparatus;

FIG. 3 is a section similar to FIG. 1, of a modified vcentrifuging device;

FIG. 4 is a view similar to FIG. 2, of the modified device;

FIG. 5a is an elevation of an end cover of the device of FIG. 3; and

FIG. 5b is a section on line 8-8 of FIG. 5a.

FIG. 1 shows an enclosure permitting the centrifuging of molten samples of pig iron. This enclosure is composed of a cylinder 1 provided with a filling opening 2 and two orifices 3, 4 obturated respectively by covers 5 and 6. These two covers 5 and 6 are clamped in place by plates 7, 8, draw rods 9, l0, and tightening screws 11 to 14 (FIG. 2).

The draw-rods 9, 10 pass through two cradles l5, l6 fixed to a circular plate 17 which is co-axial with the axis of symmetry.l8 of the enclosure. This plate 17 as it rotates carries the cradles 15, 16, the clamps, and the enclosure 1, about the axis 18. A refractory lining 19 of asbestos protects the enclosure up to the ends of the two conduits 20, 21.

The refractory asbestos lining is terminated at each end by an offset portion 22, 23 which has the effect of breaking the force of the jet of pig iron before the metal has been able to strike the cover.

The device functions as follows:

The cylinder 1, covers 5, 6, and draw rods 9, 10, are fixed to the plate 17, and the plate is rotated rapidly about the axis 18. The rotation speeds utilised are from 2,500 to 3,000 r.p.m. and the length of the conduits is determined in such a manner that the sample reaches the end of the conduit at a temperature which is a little higher than the melting point.

The liquid pig iron is poured through the orifice 2 and is immediately centrifuged. It collects at the ends of the conduits 20 and 21, and the amount of pig iron is selected in such a manner that the pig iron collected at the ends of the conduits 20, 21 is not in contact with the asbestos. The asbestos acts as a heat insulation, slowing down the cooling of the liquid pig iron during its passage from the centre of the enclosure to its end, which is the only place where the solidification of the pig should take place. On the other hand, the cylinder 1 as well as the covers 5 and 6 are metallic (for instance of steel) inorder to accelerate this cooling.

It should also be noted that lining the cylinder 1 with asbestos only on the portion of the enclosure which serves to ensure the movement of the pig up to its final place at the ends of the conduits has another advantage: it facilitates the removal of solidifed samples; it suffices to unlock the clamps and to withdraw the said samples, which are easily freed from the conduits by virtue of the contraction which they undergo during cooling. Any risk of sticking to the asbestos is avoided, so that all that remains is to smooth one of the faces of the sample before subjecting it to arcing.

From the purely constructional viewpoint, the cradles l5 and 16 may advantageously be profiled to enclose between them the cylinder 1 constituting the enclosure in which the pig iron is cast. Moreover, one can envisage connecting to the central portion of the enclosure more than two conduits of the type 20 or 21, which would make it possible to produce more than two samples simultaneously.

The solidified samples are subjected to spectral analysis. This can be done by analysis of the visible and/or ultraviolet spectrum emitted when an electric arc is set up between the pig iron and an electrode in an argon atmosphere. Alternatively, the X-ray fluorescence spectrum can be analysed, this being the mainly ultraviolet spectrum emitted when the pig iron is bombarded with X-rays.

FIGS. 3 to 5 show a modified version of the centrifuging device. In this version, the interior protection of the cylinder 1 can be effected either by a refractory tube housed in the cylinder, in the manner for example of the tube 19 (FIG. 1 or by a layer of refractory cement applied to the inner surface of the cylinder 1, for example by painting. Such a cement can have the following approximate composition:

(3)1 kg zirconium powder,

20 g bentonite, and

0.34 water.

This is mixed and left to stand for 12 h at least; then I0 ml linseed oil and 2.5 g dextrine are added and the cement is remixed, it is then ready for use.

The end covers 5 and 6 are in the form of small frusto-conical ingot moulds, whilst the orifices 3, 4 of the cylinder 1 open frustoconically. Thus an easy and auto matic removal of the pellets from the mould is obtained.

The screws 27 and 28 (FIG. 4) which engage in the respective plates 7, 8, have terminal extension rods 29, 30 which pass freely through apertured discs 31, 32 fixed on the plates 7, 8. This arrangement prevents any splash of metal from damaging the threaded parts; it is therefore ensured that the screws 27, 28 can always be easily unscrewed after centrifugation of the pellet.

One of the two covers (5 or 6) is provided with an elongated groove 24 (FIG. 5) in order to produce a pellet having a protuberance in the form of a short pin. The pin can easily be broken from the pellet and thus supply the requisite metal matter to chemical analysis. The advantage of this is that a sample is made available simultaneously for both spectral and chemical analysis, from the same substance. It is therefore advantageously ensured that results are obtained which apply to a material whose composition is the same be it for both analyses.

VY eclaim: A

1. In a method of analysing pig iron produced in a aas ll sstsps f a a. taking a sample of liquid pig iron at the taphole of said furnace;

b. pouring said liquid sample through a filling orifice into an enclosure rotating about an axis passing through said filling orifice, said enclosure being provided with at least two conduits extending substantially perpendicularly to the axis of rotation of said enclosure, said liquid sample being centrifuged in such a manner that it reaches the end of said conduits, where it solidifies in the form of pellets;

c. removing said pellets from said conduits; and

d. subjecting said pellets to spectral analysis. 

1. In a method of analysing pig iron produced in a furnace, the steps of a. taking a sample of liquid pig iron at the taphole of said furnace; b. pouring said liquid sample through a filling orifice into an enclosure rotating about an axis passing through said filling orifice, said enclosure being provided with at least two conduits extending substantially perpendicularly to the axis of rotation of said enclosure, said liquid sample being centrifuged in such a manner that it reaches the end of said conduits, where it solidifies in the form of pellets; c. removing said pellets from said conduits; and d. subjecting said pellets to spectral analysis. 